A mobile communication system performs handover so that a Mobile Station (MS) secures mobility to perform communication. The handover is to change Base Stations (BSs) while maintaining the call connection of an MS in a mobile communication system, which is unnoticed by a user of the MS. Accordingly, the MS continues to maintain call connection by performing control according to the BS change.
Extensive research has been conducted on the handover technology for the conventional 2G/3G systems. In particular, research has been conducted to prevent unnecessary frequent handover, such as a ping-pong phenomenon, in an overlapping region between two cells.
In order to overcome the above limitation, the 3GPP Rel8 (LTE) system includes UE-History information, indicating the stay time of a UE in each cell, in a field of a handover preparation information message and optimizes handover on the basis of the specific information of the UE.
However, the above method has a limitation in handover optimization because it does not use information in a neighbor cell (particularly, a handover target cell).
FIG. 1 illustrates a diagram of a handover process in a general mobile communication system.
Referring to FIG. 1, it is assumed that a Mobile Station (MS) 100 moves across an overlapping region between cells A 110, B 120 and C 130. That is, the MS 100 performs a handover from the cell B 120 to the cell C 130 immediately after performing a handover from the cell A 110 to the cell B 120. In this case, the cell A 110 cannot detect the occurrence of such an unnecessary handover (i.e., a handover to the cell B 120) for itself.
The cell C 130 can detect the occurrence of an unnecessary handover by means of the history information of the MS 100 but cannot perform handover optimization only by means of the information exchanged between cells, which is defined in the 3GPP standard specification.
That is, if moving from a point of the cell A 110 to the cell C 130 as illustrated in FIG. 1, the MS 100 performs a handover to the cell B 120 and then a handover from the cell B 120 to the cell C 130, at points A 102, B 104 and C 106 in the overlapping region between the cells A 110, B 120 and C 130. That is, the MS 100 performs a handover to the cell C 130 after performing an unnecessary handover to the cell B 120, thus degrading the performance of the mobile communication system.
What is therefore required an apparatus and method for preventing the performance degradation of the mobile communication system that may be caused by an unnecessary handover to the cell B 120, which may occur when the MS 100 moves from the cell A 110 to the cell C 130 as illustrated in FIG. 1.